It is known that many oxygen sensitive products, including food products such as meat and cheese, smoked and processed luncheon meats, as well as non-food products such as electronic components, pharmaceuticals, and medical products, deteriorate in the presence of oxygen. Both the color and the flavor of foods can be adversely affected. The oxidation of lipids within the food product can result in the development of rancidity. These products benefit from the use of oxygen scavengers in their packaging.
Some of these oxygen scavengers, typically unsaturated polymers with a transition metal catalyst, can be triggered by actinic radiation. Such materials offer the advantage of an oxygen scavenger that does not prematurely scavenge oxygen until such time as the user decides to use the oxygen scavenger in a commercial packaging environment. The oxygen scavenger is thus not triggered until it is passed through a triggering unit, typically a bank of UV lights through which an oxygen scavenger in the form of a film is passed to trigger the oxygen scavenging activity of the material. This is usually done just prior to a packaging step, in which a package having as a component the oxygen scavenger is made, with an oxygen sensitive product placed in the package prior to closure of the package to extend the shelf life of the oxygen sensitive product.
Unfortunately, triggering of the type of oxygen scavenger just described during high speed packaging applications (having a packaging line speed of greater than about 40 feet per minute) presents a challenge with conventional equipment and technology. Conventional triggering units and formulations are practically limited to a maximum line speed of about 20 feet per minute. Conventional triggering equipment is already quite large, and to achieve higher speeds with this technology would require even larger units. The size and associated costs of purchasing or leasing such equipment, maintenance costs, and the requirement of space in the processing plant to accommodate such equipment, can be economically unattractive. Some processors or potential users of oxygen scavenging film do not have room for large equipment.
Another class of oxygen scavengers, which do not require actinic triggering, and thus do not require the associated triggering equipment, are iron-based scavengers and some polymeric scavengers that are provided in active form. Such oxygen scavengers are active at the time of manufacture without triggering by actinic radiation. These also have several disadvantages, however. Some require the presence of moisture to initiate oxygen scavenging. This may not be technically attractive in packaging environments where it is otherwise undesirable or impractical to provide a moisture source to trigger the oxygen scavenger. Also, optics of the finished package can often be undesirably compromised by discoloration or pigmentation of the oxygen scavenger itself, either in its original state or after a period of oxygen scavenging activity. Processing of these oxygen scavengers in a uniformly dispersed way can also prove difficult in conventional extrusion operations. If such scavengers are not dispersed, as is the case with iron based sachets, scavenging activity may be too localized, and uniformity of scavenging may thus not be sufficient in the entire package environment to provide proper and adequate removal of oxygen from the head space of the package, and/or active barrier from subsequent ingress of oxygen from outside the package. Furthermore, oxygen scavenging sachets are unsuitable for vacuum packaging applications.
It has now been found that a solution to these problems is to trigger an oxygen scavenger with actinic radiation or heat, for example in a film converter's facility, and then store the triggered oxygen scavenger in a container such that the oxygen scavenger exhibits no substantial oxygen scavenging activity while inside the container. The stored, triggered oxygen scavenger can then be shipped to a processor. The processor can store the container until such time as the oxygen scavenger is needed for use in a packaging or other application. At that time, the triggered oxygen scavenger is removed from the container, and used as needed in a packaging or other process.
This solution avoids the cost of very large triggering equipment in a processor's plant. Less cost has to be passed on to the processor. In addition, this solution requires no additional space in the processor's plant. A greater proportion of the potential market can then access oxygen scavenging technology. Still retained is the benefit of using an oxygen scavenger whose oxygen scavenging capacity has not been largely and prematurely depleted during storage.
In addition to simply storing the triggered oxygen scavenger in a container, the inventors of this technology have also found it beneficial to store and transport that container at sub-ambient temperature conditions. The inventors have found that by combining the storage of the triggered oxygen scavenger, in an oxygen barrier container (such that the atmosphere in the container has a reduced oxygen atmosphere, achieved by e.g. gas flushing the container atmosphere with an inert gas to achieve a reduced oxygen concentration or by removing the atmosphere with a vacuum packaging system) and then storing the triggered and packaged oxygen scavenger under sub-ambient temperature storage, the potential to deliver the maximum potential oxygen scavenging capacity is improved.
The triggered oxygen scavenger can be wound onto a roll before being stored in the container, and optionally a chilled lay-on roll can be used during the winding process to lower the temperature of the triggered film before and/or during the winding operation. Alternatively, the triggered film can be wrapped around a chilled roll just prior to winding the film onto a roll. Chilled air or rolls can be used in the production of pre-triggered pouches.
Definitions
“Oxygen scavenger” and the like herein means a composition, compound, film, film layer, coating, plastisol, gasket, or the like which can consume, deplete or react with oxygen from a given environment.
“Actinic radiation” and the like herein means radiation or radiant energy that produces chemical changes. Preferred is visible or ultraviolet light, especially UV-C light, and ionizing radiation in the form of X-ray, gamma ray, corona discharge, or electron beam irradiation, capable of causing a chemical change, as exemplified in U.S. Pat. No. 5,211,875 (Speer et al.).
“Trigger” and the like refers herein to that process defined in U.S. Pat. No. 5,211,875, whereby oxygen scavenging is initiated by exposing a composition, film, etc. to actinic radiation having a wavelength of less than about 750 nm at an intensity of at least about 1.6 mW/cm2 or an electron beam at a dose of at least about 0.2 megarads, wherein after initiation the oxygen scavenging rate is at least about 0.05 cc oxygen per day per gram of oxidizable organic compound or other oxygen scavenger for at least two days after oxygen scavenging is initiated. Preferred is a method offering a short “induction period” (the time that elapses, after exposing the oxygen scavenger to a source of actinic radiation, before initiation of the oxygen scavenging activity begins) so that the oxygen scavenger can be triggered at or immediately prior to use during filling of a package with an oxygen sensitive material. In some instances it is known that oxygen scavengers comprising unsaturated polymers with a transition metal catalyst, can be triggered or activated by the heat of the extrusion or blending process, or a subsequent process of forming a packaging article from the composition. Such compositions and methods are disclosed in U.S. Pat. No. 6,610,215 (Cai et al.) incorporated herein by reference as if set forth in full. In these cases, the composition or article is immediately active and is expected to benefit from the storage methods described herein. In addition, such compositions and methods of initiating an oxygen scavenging composition are well suited to the business method described herein.
Thus, “trigger” or the like refers to exposing an oxygen scavenger to actinic radiation as described above or sufficient heat during processing to activate the scavenging reaction; “initiation” refers to the point in time at which oxygen scavenging actually begins; and “induction time” refers to the length of time, if any, between triggering and initiation.
“Container” herein means an enclosure such as a bag, pouch, vessel, sleeve, or the like, that is capable of enclosing or packaging an oxygen scavenger in such a way that the oxygen scavenger exhibits no substantial oxygen scavenging activity while inside the container. “No substantial oxygen scavenging activity while inside the container” herein means that while the oxygen scavenger is in the container, the oxygen scavenging rate of the oxygen scavenger is either 0, or else less than a rate that would deplete the oxygen scavenging activity of the oxygen scavenger, while in the container, to an extent that would render the oxygen scavenger unusable for its intended application. Preferred is an oxygen scavenging rate, while in the container, of less than 0.03 cc oxygen per day per gram of oxidizable organic compound or other oxygen scavenger for at least two days while the oxygen scavenger is in the container.
“Film” herein means a film, laminate, sheet, web, coating, or the like, which can be used to package an oxygen sensitive product. The film can be used as a component in a rigid, semi-rigid, or flexible product, and can be adhered to non-polymeric or non-thermoplastic substrates such as paper or metal. The film can also be used as a coupon or insert within a package.
“Polymer” and the like herein means a homopolymer, but also copolymers thereof, including bispolymers, terpolymers, etc.
“Sub-ambient” and the like herein refers to temperatures of 25° C. or less.
“Refrigerated” and the like herein refers to temperatures of 10° C. or less.
“Structure” and the like herein refers to a film, web, wall, etc. that includes an oxygen scavenger as a component or layer thereof.
All compositional percentages used herein are presented on a “by weight” basis, unless designated otherwise.